1. Field of the Invention
The present invention is directed generally to an information extraction apparatus, an information extraction method, an information-extraction computer program product, and a storage medium.
2. Description of the Related Art
Information embedding techniques of additionally embedding some type of information in image data to be printed, such as a document image, when the image data is printed have conventionally been known. Some information embedding techniques use dot patterns.
For instance, in one of such techniques that use dot patterns, desired information is embedded in a printed material by printing a matrix of dot patterns, each of which is a minimum information unit, in a background of the printed material, and the embedded information is extracted by reading the printed material with a scanner or the like, and identifying each dot pattern in the thus-read image to restore the information (see, for instance, Japanese Patent Application Laid-open No. 2006-238119).
For identification of dot patterns by using such a technique as discussed above, it is necessary to specify a position of each dot pattern first, which can be attained by, as is disclosed in Japanese Patent Application Laid-open No. 2006-238119, approximating each of horizontal rows of dot patterns and vertical rows of dot patterns by a straight line, and calculating a point of intersection between the thus-approximated straight lines.
There can be employed another technique of approximating each of horizontal rows of dot patterns and vertical rows of the dot patterns by a polygonal line or a curve and calculating a point of intersection between the thus-approximated polygonal lines or curves so as to allow for distortion that can be mechanically caused in an image read by a scanner, or the like, as disclosed in Japanese Patent Application Laid-open No. 2006-238119.
A method for calculating a point of intersection between curves is disclosed in, for instance, Japanese Patent No. 2734643.
However, processing for approximating rows of dot patterns by curves and calculating points of intersection between the curves by using such a method as disclosed in Japanese Patent No. 2734643 places a higher load than that placed by processing for calculating points of intersection between straight lines, which can make information extraction time consuming.
Approximation of rows of dot patterns is generally performed by using some of the dot patterns that are found to match prepared-for-search dot patterns by template matching. Accordingly, in approximating a row of dot patterns by a curve, as the interval between the thus-found dot patterns increases, the error between the actual row of the dot patterns and an approximated curve disadvantageously increases.